Mainframes occupied an interesting spot in the American imagination. The mainframe, in the movies, was an incantation: it conjured up all the mysterious power and glory of technology. The mainframe could compute not just faster, but other.
The mainframe was an oracle that had secrets and power, but it was locked away in the bowels of a corporation or government, hard to reach physically, hard to reach digitally. The quest to get into the mainframe -- by either means of egress -- could form the backbone of a movie, and it took a hero, or as often, a classic Lord-of-the-Rings-style team of wizards and warriors, tricksters and average Joes. I always loved that the stories tended to unite the nerdy hackers with the brawny people of action, both their skills required to acquire the power within; it was a recognition of the dual nature of computers as physical objects and hosts for digital information. And so often, it seemed, the action turned on getting into the space that connected these two realities. The mainframe was unhackable unless they were in the room, in which case, it was simple. Or they couldn't break into the room without a hacker using the mainframe itself to help the physical assault.